The invention relates to an expansible fixing plug having torsional stiffness, the expansible fixing plug extending in a longitudinal direction.
Such an expansible fixing plug is known from DE 39 21 733 A1. The known expansible fixing plug is manufactured as a two-material fixing plug from two materials of different hardness. In simplified terms, it consists of two sleeves assembled one inside the other by injection moulding, which are divided by a longitudinal slit into two expansible elements running in the longitudinal direction of the fixing plug. The outer sleeve consists of a relatively hard material and the inner sleeve consists of a relatively soft material. By screwing in an expansion screw, the expansible elements are expanded and the expansible fixing plug is anchored in a drilled hole. The hard material arranged on the outer surface of the fixing plug produces good anchoring with high retention force in the drilled hole, whilst the effect of the soft material, into which the expansion screw is screwed, is that the insertion torque of the expansion screw is low.
The known expansible fixing plug has the disadvantage that the screw can run off centre as it is being screwed in, that is, it screws off-axis into the expansible fixing plug and passes through the longitudinal slit that divides the fixing plug into the expansion elements and out of the side of the fixing plug. A further disadvantage of the known expansible fixing plug is its low torsional stiffness; screwing in the expansion screw causes the rear end of the fixing plug to twist relative to the leading end of the fixing plug.
The invention is based on the problem of constructing a two-material expansible fixing plug of the kind mentioned in the introduction so that it has a high torsional stiffness and as the expansion screw is screwed in it runs in the longitudinal direction of the fixing plug.
That problem is solved in accordance with the invention by the features of claim 1.
The expansible fixing plug according to the invention has expansion fingers, which run substantially in the longitudinal direction of the fixing plug and which consist of the relatively hard material. The expansion fingers of the relatively hard material are arranged at the outer circumference of the expansible fixing plug. In a hole drilled in a solid building material, the expansion fingers are pressed by the expansion screw against the wall of the drilled hole as the expansion screw is screwed into the expansible fixing plug, and the expansible fixing plug is consequently anchored in the drilled hole with high retention force. The relatively soft material joins the expansion fingers to one another circumferentially, the joint being made preferably continuous in the longitudinal direction of the expansible fixing plug, although it may alternatively be discontinuous. The soft material presents only slight resistance to expansion of the expansion fingers, so that expansion is not appreciably impeded and the insertion torque of the expansion screw is not appreciably increased. At the same time, the soft material increases the torsional stiffness of the expansible fixing plug. Moreover, the relatively soft material forms an expansion hole that is closed circumferentially and in this way prevents the screw from being screwed off-axis into the expansible fixing plug and emerging through the side of the fixing plug. Moreover, the relatively soft material reduces the insertion torque of the expansion screw.
When anchoring the expansible fixing plug according to the invention in a hollow building material, the relatively soft material joining the expansion fingers circumferentially limits the expansion of the expansion fingers. Screwing the expansion screw into the expansible fixing plug in a hollow building material causes the expansion fingers to bow out in a curve in the longitudinal direction of the fixing plug, and the expansible fixing plug is anchored in the hollow building material by interlocking engagement. The relatively soft material joining the expansion fingers circumferentially prevents the expansion fingers from buckling or becoming tangled together in a knot. The insertion torque of the expansion screw is prevented, after an increase, from falling to a low value again, as would be the case if the expansion fingers buckled or became entangled. A torque that decreases after an initial increase conveys the impression of poor anchoring and is therefore undesirable.
In one configuration of the invention, the cross-sectional area of the expansion fingers is larger in the region of the leading end of the expansible fixing plug and smaller in a rear part of the expansion zone; the cross-sectional area of the expansion fingers decreases over the expansion zone from the front end towards the rear. The effect of the smaller cross-sectional area of the expansion fingers consisting of the relatively hard material in the rear part of the expansion zone is that the insertion torque of the expansion screw at the start of screwing-in is low. The effect of the large cross-sectional area of the expansion fingers consisting of the relatively hard material in the region of the leading end of the expansible fixing plugs is that expansion is considerable and consequently good anchoring with high retention force is achieved. This feature optimizes the relationship between insertion torque, expansion, and anchoring force.
The leading end of the expansible fixing plug preferably consists entirely of the relatively hard material. In particular, a ring or hollow cylinder of the relatively hard material is formed at the leading end of the expansible fixing plug, into which the expansion screw is screwed as the expansible fixing plug is expanded. This configuration of the invention has the advantage of good anchoring. A further advantage of this configuration of the invention is that the leading end of the expansible fixing plug consisting entirely of the relatively hard material forms a kind of nut, by means of which the expansible fixing plug is axially compressed when the expansion fingers are bowed out in a hollow building material and hence become disengaged from the screw thread of the expansion screw.
The relatively soft material joining the expansion fingers circumferentially forms circumferentially dilatable dilatation zones. In this connection, in one configuration of the invention the dilatability in the circumferential direction of the expansible fixing plug is achieved by a folded portion of the relatively soft material joining the expansion fingers, the folded portion having folds running in the longitudinal direction of the fixing plug. The dilatability is here achieved by a change in shape, namely an opening-out, of the folded portion, and not or only partly by a material dilatation of the relatively soft material. This has the advantage of a greater dilatability and a defined limit of the dilatation circumferentially. The effect of this defined limitation of the dilatation is a defined limited width of the bowing of the expansion fingers on expansion of the expansible fixing plug in a hollow building material.
In one configuration of the invention, expansion tongues are formed from the relatively soft material, into which the expansion fingers consisting of the relatively hard material are embedded. The effect of having the expansion tongues of the relatively soft material in addition to the expansion fingers of the relatively hard material is that the expansible fixing plug adapts better to a drilled hole. In a hole drilled in a hard solid building material, the relatively soft material is displaced by screwing in the expansion screw and consequently too high an insertion torque is prevented. The expansion fingers of the hard material effect good anchoring with high retention force. In a hole drilled in less hard building material, the effect of the expansion tongues is a greater expansion of the expansible fixing plug and consequently likewise good anchoring of the expansible fixing plug in the building material. Moreover, the expansion tongues of the relatively soft material mould themselves to irregularities and the like in the wall of a drilled hole and hence also effect good anchoring with high retention force.